In a strapping tool of a type used to apply a steel strap in a tensioned loop around a package and to join the strap via a series of interlocking joints comprising interlockable shoulders punched into overlapped ends of the strap, an actuating handle is provided, which is arranged to be manually oscillated. The handle rotates an output shaft, which actuates a series of cams, via an input shaft, to which the handle is coupled, and intermediate gears. The cams drive a series of punches, which punch interlockable shoulders into overlapped ends of the strap. Tremper et al. U.S. Pat. No. 4,825,512 provides a recent example of such a strap having such a series of interlocking joints.
Moreover, in a strapping tool of the type noted above, a mechanism is provided for converting oscillatory motion of the actuating handle to unidirectional rotation of the output shaft. Typically, heretofore, the converting mechanism has employed a unidirectional clutch to couple the handle to the input shaft upon forward motion of the handle and to decouple the handle from the input shaft upon reverse motion of the handle. Thus, reverse motion of the handle has been unproductive, except to reset the handle for forward motion. Typically, moreover, two strokes of forward motion of the handle have been required to provide one complete rotation of the output shaft for one complete stroke of the punches.
A mechanism employing bevel gears and ratchet wheels for converting oscillatory rotation of an input shaft to unidirectional rotation of an output shaft is known. Such a mechanism is exemplified in Grafstein et al., Pictorial Handbook of Technical Devices, Chemical Publishing Co., Inc. (1971) at pages 60 and 61. However, if it were employed in a strapping tool of the type noted above, such a mechanism would not be entirely satisfactory. Such a mechanism does not limit oscillatory rotation of the input shaft to any specific range and does not limit unidirectional rotation of the output shaft to any specific range. In a strapping tool of the type noted above, however, it is desirable to limit oscillatory rotation of the input shaft to a specific range (e.g. approximately 180.degree.) and to limit unidirectional rotation of the output shaft to one complete rotation in each operating cycle.
An improved mechanism employing three bevel gears for converting oscillatory rotation of an input shaft to unidirectional rotation of an output shaft, as in a strapping tool of the type noted above, is disclosed in Nix U.S. Pat. No. 5,136,888. As disclosed therein, a first gear and a second gear are mounted around the input shaft so as to permit relative rotation between each of the first and second gears and the input shaft. Also, a third gear intermeshed with those two gears is coupled to the output shaft so as to enable conjoint rotation of the third bevel gear and the output shaft. Further, each gear mounted around the input shaft can be alternately coupled to and uncoupled from the input shaft via an associated pawl disposed in a socket in the input shaft and biased toward an operative position, in which the associated pawl is extended into a recess in a bearing surface of such gear.